A polarized optical beam, for example laser output, is exposed to distortions when it is transmitted through an optical fiber. One type of distortion relates to uncontrolled changes that occur in the state of polarization of the optical beam passing through the optical fiber. The state of polarization of the input beam is disrupted by the parasitic effect of the fiber.
A prior art solution for maintaining the state of polarization is to use a special optical fiber that maintains the state of polarization of the light as it passes through the fiber.
A drawback of that solution is the very high cost of the special optical fiber used.
In U.S. 20020135874 (Li), and U.S. Pat. No. 5,164,854 (Takanashi), polarization recovery systems were disclosed where an initial light beam is split into two beams, one of P polarization state and the other in S polarization state. Li suggests this treatment in order to enhance illumination of an LCD imager. Takanashi suggests a converter for randomly-polarized light to linearly polarized light, where the initial light beam is separated into two beams in a first polarization state and a second (orthogonal) polarization state, and changing the second polarization state to a third polarization state which is identical to the first polarization state. Both these treatments are aimed at producing linearly polarized light. They do not suggest nor are capable of recovering initial polarization state of a light beam that was passed through an optical fiber undergoing, as it traverses the fiber, parasitic distortions of its polarization state. Furthermore, they do not combine the two reproduced primary-separated orthogonal polarized beams into a single beam. It is important to note that the above mentioned invention does not deal with sensing of the light processed in these systems, but rather use the light for spatial illumination. The human eye is insensitive for short-term fluctuations in intensity of light it sees (for periods less then 50 milliseconds), whereas the invention of the present invention seeks to provide a system for stabilizing an output light signal for measurement purposes, and hence is concerned with short-term fluctuations much shorter than those mentioned above.
Use of a special fiber can be avoided if the state of polarization is allowed to fluctuate as the beam passes through the fiber, and then reconstructed from the fiber output.
In the present invention the polarization state of the fiber input is recovered from the fiber output using a specially designed device, which produces two beams of equal polarity and equal power.
Therefore, it is a main object of the present invention to provide a method and a system that takes as input an optical beam that has been transmitted through a general-purpose multi-mode or single-mode optical fiber and produces an output beam whose state of polarization is the same (linearly polarized) as that of the optical beam before the optical beam entered the fiber, and whose power is in direct proportion to the input power function versus time.